The repair of bone defects and augmentation of existing bone often require the use of permanent bio-resorbable materials. Such materials may include autogenous bone graft, allogeneic graft, allogeneic bone graft, or alloplastic materials inclusive of various calcium phosphate ceramics, calcium phosphate cements, calcium sulfate materials, bioglass materials, and composites or other combinations thereof. Calcium sulfate, which is a form of plaster of paris, is a fully bioresorbable material which, for sometime, has been commonly used in cement and pellet form to repair bone defects.
When calcium sulfate is used as a cement to fill a bone void, fracture, or other defect, this material dissolves at a rapid rate, i.e., approximately one millimeter per week from the exterior of the cement towards the center thereof. Research of the present inventors has shown that this material causes precipitation of calcium phosphate deposits as it is resorbed at the surgical site. These precipitates, it has been shown, stimulate and direct the formation of new bone. On the other hand, it is important for purposes of optimal result that calcium sulfate, calcium phosphate, or any other bone repair material stay at the surgical site for a considerable period of time in order to inhibit soft tissue filling of the defect and to stimulate bone repair. However, currently used calcium sulfate materials are resorbed by human bone within two to seven weeks, depending upon the calcium sulfate form and the particular surgical site, which cannot be retained at the site for longer periods. As noted, such material is resorbed faster than it can be replaced by new bone thereby reducing its value to both patient and practitioner.
As such, the principal concern and difficulty expressed by practitioners (such as orthopedics or maxiofacial surgeons) are that calcium sulfate materials bio-resorb or dissolve too rapidly at a surgical or a recipient site, and, thereby, outpace the formation of new bone in human patients. Therefore, a need arises for improved calcium sulfate based compositions which can resorb at the recipient site in a rate desirably matching the rate bone growth.
The present invention relates to an implant composition having controlled resorption rate in vivo for stimulating bone growth, a method of making the implant composition, and a kit of implant materials.
In one aspect of the present invention, an implant composition having controlled resorption rate comprises a calcium sulfate compound, polymer containing particles, and a setting agent for setting the calcium sulfate compound and the polymer containing particles into a heterogeneous solid composition. Upon setting, the calcium sulfate compound forms a matrix and the polymer containing particles settled within the matrix.
In another aspect, the present invention comprises a method of using implant materials to make the inventive implant composition for bone augmentation and bone defect reparation. The method comprises the steps of: (a) mixing a calcium sulfate compound and polymer containing particles with a setting agent into a mixture, (b) applying the mixture, either by filling in a recipient site with the mixture, or by coating the mixture on a surface of a surgical implant prior to introducing the surgical implant into the recipient site, and (c) setting the mixture into a heterogeneous solid composition.
In a further aspect, the present invention relates to a kit of implant materials for bone augmentation and bone defect reparation. The kit comprises (a) dry powder of a calcium sulfate compound, and (b) polymer containing particles. The kit can further comprise a setting agent packed in a container, and instructions on how to use the kit for preparing the implant composition.
It is accordingly an object of the present invention to provide an implant composition for the repair and augmentation of bone defects.
It is another object of the invention to provide an implant composition having controllable resorption rate in vivo, wherein the rate of resorption can be substantially matched to the rate of bone growth in a specific medical or dental application.
It is a further object of the invention to provide implant materials and a method for making the implant composition.
The above and yet other objects and advantages of the present invention will become apparent from the hereinafter set forth Brief Description of the Drawings and Detailed Description of the Invention.